The incorporation of [3H]fucose into the novel fucosides glucosyl-fucosyl-threonine(FL4a) and fucosyl-threonine(FL3a) has been utilized in this laboratory and by others to predict the tumorigenic and metastatic potential of transformed rat fibroblasts and transformed mouse epithelial cells. During the past year, we have focused on chemical and metabolic characterization of the parent glycoproteins of FL3a and FL4a to better understand the basis for the decreased FL4a and FL3a levels in cancer cells. Protein fractions were separated and purified by gel filtration and polyacrylamide gel electrophoresis from [3H]fucose-labeled cells. Fractions ranging from greater than 250,000 daltons to less than 50,000 daltons were analyzed for 0-linked fucosecontaining glycoproteins after mild alkaline borohydride treatment. A number of protein fractions contained 0-linked fucose constituents. Moreover, a reduced level of these constituents was observed in the oncogenically transformed cells as compared with their normal counterparts. This latter observation presents an interesting parallel to our previously reported finding of a marked reduction in the level of FL4a in transformed cells. In addition, initial studies indicate that some of the proteins with 0-linked fucose are released from the cells. The possible role of secretion in the reduction in the level of FL4a in cancer cells is currently being examined.